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</tr></table><h1 class="title">A Trivial Example<br /><span class="subtitle"></span>
</h1>
<p>The application in this example has a log-view that displays messages sent by further instances of the same application.</p>
<p>The example demonstrates the use of the <a href="qtsingleapplication.html">QtSingleApplication</a> class to detect and communicate with a running instance of the application using the sendMessage() API. The messageReceived() signal is used to display received messages in a <a href="http://qt.nokia.com/doc/4.6/qtextedit.html">QTextEdit</a> log.</p>
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 #include &lt;qtsingleapplication.h&gt;
 #include &lt;QtGui/QTextEdit&gt;

 class TextEdit : public QTextEdit
 {
     Q_OBJECT
 public:
     TextEdit(QWidget *parent = 0)
         : QTextEdit(parent)
     {}
 public slots:
     void append(const QString &amp;str)
     {
         QTextEdit::append(str);
     }
 };

 #include &quot;main.moc&quot;

 int main(int argc, char **argv)
 {
     QtSingleApplication instance(argc, argv);</pre>
<p>The example has only the <tt>main</tt> entry point function. A <a href="qtsingleapplication.html">QtSingleApplication</a> object is created immediately.</p>
<pre>     if (instance.sendMessage(&quot;Wake up!&quot;))
         return 0;</pre>
<p>If another instance of this application is already running, sendMessage() will succeed, and this instance just exits immediately.</p>
<pre>     TextEdit logview;
     logview.setReadOnly(true);
     logview.show();</pre>
<p>Otherwise the instance continues as normal and creates the user interface.</p>
<pre>     instance.setActivationWindow(&amp;logview);

     QObject::connect(&amp;instance, SIGNAL(messageReceived(const QString&amp;)),
                      &amp;logview, SLOT(append(const QString&amp;)));

     return instance.exec();</pre>
<p>The <tt>logview</tt> object is also set as the application's activation window. Every time a message is received, the window will be raised and activated automatically.</p>
<p>The messageReceived() signal is also connected to the <a href="http://qt.nokia.com/doc/4.6/qtextedit.html">QTextEdit</a>'s append() slot. Every message received from further instances of this application will be displayed in the log.</p>
<p>Finally the event loop is entered.</p>
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